Wednesday, July 20, 2016

Don't panic. Of course it isn't. Stop typing that angry letter to the editor and read on. I just picked that title because it's clickbait and these days that's all that matters, right?

With the release of libinput 1.4 and the newest feature to add tablet pad mode switching, we've now finished the TODO list we had when libinput was first conceived. Let's see what we have in libinput right now:

keyboard support (actually quite boring)

touchscreen support (actually quite boring too)

support for mice, including middle button emulation where needed

support for trackballs including the ability to use them rotated and to use button-based scrolling

touchpad support, most notably:

proper multitouch support on touchpads [1]

two-finger scrolling and edge scrolling

tapping, tap-to-drag and drag-lock (all configurable)

pinch and swipe gestures

built-in palm and thumb detection

smart disable-while-typing without the need for an external process like syndaemon

more predictable touchpad behaviours because everything is based on physical units [2]

a proper API to allow for kinetic scrolling on a per-widget basis

tracksticks work with middle button scrolling and communicate with the touchpad where needed

tablet support, most notably:

each tool is a separate entity with its own capabilities

the pad itself is a separate entity with its own capabilities and events

mode switching is exported by the libinput API and should work consistently across callers

a way to identify if multiple kernel devices belong to the same physical device (libinput device groups)

The side-effect of libinput is that we are also trying to fix the rest of the stack where appropriate. Mostly this meant pushing stuff into systemd/udev so far, with the odd kernel fix as well. Specifically the udev bits means we

know the DPI density of a mouse

know whether a touchpad is internal or external

fix up incorrect axis ranges on absolute devices (mostly touchpads)

try to set the trackstick sensitivity to something sensible

know when the wheel click is less/more than the default 15 degrees

And of course, the whole point of libinput is that it can be used from any Wayland compositor and take away most of the effort of implementing an input stack. GNOME, KDE and enlightenment already uses libinput, and so does Canonical's Mir. And some distribution use libinput as the default driver in X through xf86-input-libinput (Fedora 22 was the first to do this). So overall libinput is already quite a success.

Finally: libinput was started by Jonas Ådahl in late 2013, so it's already over 2.5 years old. And the git log shows we're approaching 2000 commits and a simple LOCC says over 60000 lines of code. I would also like to point out that the vast majority of commits were done by Red Hat employees, I've been working on it pretty much full-time since 2014 [3]. libinput is another example of Red Hat putting money, time and effort into the less press-worthy plumbing layers that keep our systems running. [4]

[1] Ironically, that's also the biggest cause of bugs because touchpads are terrible. synaptics still only does single-finger with a bit of icing and on bad touchpads that often papers over hardware issues. We now do that in libinput for affected hardware too.
[2] The synaptics driver uses absolute numbers, mostly based on the axis ranges for Synaptics touchpads making them unpredictable or at least different on other touchpads.
[3] Coincidentally, if you see someone suggesting that input is easy and you can "just do $foo", their assumptions may not match reality
[4] No, Red Hat did not require me to add this. I can pretty much write what I want in this blog and these opinions are my own anyway and don't necessary reflect Red Hat yadi yadi ya. The fact that I felt I had to add this footnote to counteract whatever wild conspiracy comes up next is depressing enough.

Friday, July 15, 2016

More and more distros are switching to libinput by default. That's a good thing but one side-effect is that the synclient tool does not work anymore [1], it just complains that "Couldn't find synaptics properties. No synaptics driver loaded?"

What is synclient? A bit of history first. Many years ago the only way to configure input devices was through xorg.conf options, there was nothing that allowed for run-time configuration. The Xorg synaptics driver found a solution to that: the driver would initialize a shared memory segment that kept the configuration options and a little tool, synclient (synaptics client), would know about that segment. Calling synclient with options would write to that SHM segment and thus toggle the various options at runtime. Driver and synclient had to be of the same version to know the layout of the segment and it's about as secure as you expect it to be. In 2008 I added input device properties to the server (X Input Extension 1.5 and it's part of 2.0 as well of course). Rather than the SHM segment we now had a generic API to talk to the driver. The API is quite simple, you effectively have two keys (device ID and property number) and you can set any value(s). Properties literally support just about anything but drivers restrict what they allow on their properties and which value maps to what. For example, to enable left-finger tap-to-click in synaptics you need to set the 5th byte of the "Synaptics Tap Action" property to 1.

xinput, a commandline tool and debug helper, has a generic API to change those properties so you can do things like xinput set-prop "device name" "property name" 1 [2]. It does a little bit under the hood but generally it's pretty stupid. You can run xinput set-prop and try to set a value that's out of range, or try to switch from int to float, or just generally do random things.

We were able to keep backwards compatibility in synclient, so where before it would use the SHM segment it would now use the property API, without the user interface changing (except the error messages are now standard Xlib errors complaining about BadValue, BadMatch or BadAccess). But synclient and xinput use the same API to talk to the server and the server can't tell the difference between the two.

Fast forward 8 years and now we have libinput, wrapped by the xf86-input-libinput driver. That driver does the same as synaptics, the config toggles are exported as properties and xinput can read and change them. Because really, you do the smart work by selecting the right property names and values and xinput just passes on the data.
But synclient is broken now, simply because it requires the synaptics driver and won't work with anything else. It checks for a synaptics-specific property ("Synaptics Edges") and if that doesn't exists it complains with "Couldn't find synaptics properties. No synaptics driver loaded?". libinput doesn't initialise that property, it has its own set of properties. We did look into whether it's possible to have property-compatibility with synaptics in the libinput driver but it turned out to be a huge effort, flaky reliability at best (not all synaptics options map into libinput options and vice versa) and the benefit was quite limited. Because, as we've been saying since about 2009 - your desktop environment should take over configuration of input devices, hand-written scripts are dodo-esque.

So if you must insist on shellscripts to configure your input devices use xinput instead. synclient is like fsck.ext2, on that glorious day you switch to btrfs it won't work because it was only designed with one purpose in mind.

[1] Neither does syndaemon btw but it's functionality is built into libinput so that doesn't matter.
[2] xinput set-prop --type=int --format=32 "device name" "hey I have a banana" 1 2 3 4 5 6 and congratulations, you've just created a new property for all X clients to see. It doesn't do anything, but you could use those to attach info to devices. If anything was around to read that.

Thursday, July 14, 2016

xinput is a commandline tool to change X device properties. Specifically, it's a generic interface to change X input driver configuration at run-time, used primarily in the absence of a desktop environment or just for testing things. But there's a feature of xinput that many don't appear to know: it resolves device and property names correctly.
So plenty of times you see advice to run a command like this:

xinput set-prop 15 281 1

This is bad advice, it's almost impossible to figure out what this is supposed to do, it depends on the device ID never changing (spoiler: it will) and the property number never changing (spoiler: it will). Worst case, you may suddenly end up setting a different property on a different device and you won't even notice. Instead, just use the built-in name resolution features of xinput:

This command will work regardless of the device ID for the touchpad and regardless of the property number. Plus it's self-documenting. This has been possible for many many years, so please stop using the number-only approach.

Monday, July 11, 2016

In an earlier post, I explained how we added graphics tablet pad support to libinput. Read that article first, otherwise this article here will be quite confusing.

A lot of tablet pads have mode-switching capabilities. Specifically, they have a set of LEDs and pressing one of the buttons cycles the LEDs. And software is expected to map the ring, strip or buttons to different functionality depending on the mode. A common configuration for a ring or strip would be to send scroll events in mode 1 but zoom in/out when in mode 2. On the Intuos Pro series tablets that mode switch button is the one in the center of the ring. On the Cintiq 21UX2 there are two sets of buttons, one left and one right and one mode toggle button each. The Cintiq 24HD is even more special, it has three separate buttons on each side to switch to a mode directly (rather than just cycling through the modes).

In the upcoming libinput 1.4 we will have mode switching support in libinput, though modes themselves have no real effect within libinput, it is merely extra information to be used by the caller. The important terms here are "mode" and "mode group". A mode is a logical set of button, strip and ring functions, as interpreted by the compositor or the client. How they are used is up to them as well. The Wacom control panels for OS X and Windows allow mode assignment only to the strip and rings while the buttons remain in the same mode at all times. We assign a mode to each button so a caller may provide differing functionality on each button. But that's optional, having a OS X/Windows-style configuration is easy, just ignore the button modes.

A mode group is a physical set of buttons, strips and rings that belong together. On most tablets there is only one mode group but tablets like the Cintiq 21UX2 and the 24HD have two independently controlled mode groups - one left and one right. That's all there is to mode groups, modes are a function of mode groups and can thus be independently handled. Each button, ring or strip belongs to exactly one mode group. And finally, libinput provides information about which button will toggle modes or whether a specific event has toggled the mode. Documentation and a starting point for which functions to look at is available in the libinput documentation.

Mode switching on Wacom tablets is actually software-controlled. The tablet relies on some daemon running to intercept button events and write to the right sysfs files to toggle the LEDs. In the past this was handled by e.g. a callout by gnome-settings-daemon. The first libinput draft implementation took over that functionality so we only have one process to handle the events. But there are a few issues with that approach. First, we need write access to the sysfs file that exposes the LED. Second, running multiple libinput instances would result in conflicts during LED access. Third, the sysfs interface is decidedly nonstandard and quite quirky to handle. And fourth, the most recent device, the Express Key Remote has hardware-controlled LEDs.

So instead we opted for a two-factor solution: the non-standard sysfs interface will be deprecated in favour of a proper kernel LED interface (/sys/class/leds/...) with the same contents as other LEDs. And second, the kernel will take over mode switching using LED triggers that are set up to cover the most common case - hitting a mode toggle button changes the mode. Benjamin Tissoires is currently working on those patches. Until then, libinput's backend implementation will just pretend that each tablet only has one mode group with a single mode. This allows us to get the rest of the userstack in place and then, once the kernel patches are in a released kernel, switch over to the right backend.